The invention disclosed herein describes thermosetting resin compositions useful as a matrix resin for electrical substrate applications. The thermosetting polymers are characterized by exceptional adhesion to copper foil combined with excellent thermal and electrical performance. This combination of properties is not achievable with compositions of the prior art.
The thermosetting resin compositions disclosed in U.S. Pat. No. 5,223,568 of Landi et al. comprise a polybutadiene or polyisoprene resin which is a liquid at room temperature and has a molecular weight less than 5,000 combined with a solid butadiene or isoprene containing polymer capable of cross-linking with the former polybutadiene or polyisoprene resin. Such compositions are described as generally useful for making electrical substrate materials; however, cure temperatures in excess of 250.degree. C. are employed. These cure temperatures exceed the limitations of most commercially available and cost-effective equipment.
U.S. Pat. No. 5,571,609 of St. Lawrence et al. describes an electrical substrate material similar to Landi et al. but with incorporation of woven glass fabric and particulate filler. The electrical substrates formed from these compositions afford copper foil adhesions (peel bonds) that range from 2.1 to 5 pounds per inch width via test method IPC-TM-650 2.4.8 on one ounce per square foot copper foil. Peel bonds in this range are marginal for many electrical substrate applications. Low peel bonds can render subsequently fabricated electrical circuits with poor reliability and cause failures during high temperature soldering and reflow soldering operations.
A need continues to exist for a thermosetting resin composition useful as a matrix resin for an electrical substrate capable of being manufactured on commercially available high-speed processing equipment such as described in U.S. Pat. Nos. 4,587,161 and 4,803,022 of Barrell et. al., preferably at cure temperatures of less than about 250.degree. C., more preferably less than about 180.degree. C. It is especially desirable to have electrical substrates made from compositions having high glass transition temperatures, e.g., greater than about 150.degree. C., and having high levels of adhesion (e.g., peel bonds over about 7 pounds per inch width for one ounce per square foot copper foil) to metal foil, preferable copper foil. Additionally, a need exists for compositions having Theological properties suitable for continuous lamination without the addition of solvents. Compositions that require solvents for lamination can have deficiencies associated with the incomplete removal of the solvent during the impregnation process. Additionally, the environmental emission and personal exposure of some of the most commonly used solvents can be of considerable concern.
A need continues to exist for thermosetting resin compositions with excellent electrical properties suitable for use in high frequency applications. For a polymer dielectric to be suitable for use at broadband high frequencies, it is highly desired for the dielectric constant to be stable over decades of frequency and over the environmental extremes of humidity and temperature.